High-crystalline-quality epitaxial films of wurtzite AlN were grown by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). The lattice strain of the films was analyzed by high-resolution X-ray diffraction and the E2 (high)-phonon frequency was observed by Raman scattering. Data analysis for wide ranges of lattice strains and phonon-peak shifts yielded a precise biaxial stress coefficient of this phonon mode, -4.04±0.3 cm-1/GPa. Furthermore, the deformation potential constant was accurately determined from the biaxial stress coefficient.
The growth conditions and interface microstructure of AlN on sapphire grown using a nucleation layer (NL) have been studied. The AlN layer with NL-AlN grown at 1100 °C exhibits a smooth surface morphology. The epilayer has a small amount of tilting but the twisting is large. For the AlN layer with NL-AlN grown at 1250 °C, the twisting is reduced, but the surface is rough owing to the mixing of crystallographic polarity. The origins of AlN inversion domains are discussed by considering the microstructures observed by transmission electron microscopy (TEM), with the ultimate aim of growing a high-quality AlN layer.
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